The present invention relates generally to liquid level measuring systems for fuel storage tanks and more particularly to a new and improved capacitance probe and filter assembly for such a system.
In liquid level measuring systems such as the type disclosed in commonly assigned U.S. Pat. No. 4,349,882 to Asmundsson et al, the height of fuel in an underground tank is measured for accounting and/or leak detection purposes utilizing a capacitance probe. In Asmundsson et al, a multi-segment capacitance probe is utilized in combination with a microcomputer for repeatedly periodically measuring the capacitance of each segment of the probe and calculating the level and volume of fuel in the tank using capacitance and volume calibration constants automatically updated by the computer from the measured capacitance data and from fuel delivery data automatically fed to the microcomputer.
The presence of water intermixed in the fuel in the capacitance probe varies the capacitance characteristics of the fuel depending upon the amount of water and thereby affects the accuracy of the level measurement as calculated from the capacitance measurements. Generally, the presence of water in the fuel will increase the capacitance measurement primarily due to the conductivity of water and its effective reduction of the dielectric gap of the capacitor. Additionally, the presence of water in the fuel facilitates microbal growth and reproduction which may also vary the capacitance value of the fuel.
Accordingly, it is a primary object of the present invention to provide a new and improved capacitance probe for high accuracy liquid level measurements.
It is a further object of the invention to provide a capacitance probe which significantly reduces the intrusion of water into the capacitor annulus of the capacitance probe.
A still further object of the invention is to provide a new and improved filter assembly for a capacitance probe for removing water from the fuel entering the capacitance probe.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.